Kinetic and structural investigations of deeply undercooled Zr-based bulk metallic glass forming liquids

近年来，对各种多组分玻璃形成液的研究表明，平衡熔体中的易碎液体行为与玻璃态下的强液体行为之间存在着差异。这归因于两个不同的液-液(L-L)相之间的多晶型液-液转变，每个液相都表现出不同的热力学和动力学特征。使用Couette流变仪，Busch和他的同事观察到了Zr41.2Ti13.8Cu12.5Ni10.0Be22.5(Vit1)的直接强脆转变。为了扩展这项工作，萨尔布吕肯金属材料教席和Köln空间材料物理研究所的小组联合研究了部分锆基金属玻璃形成液体的可能的S-F相变。本项目致力于通过比较常规实验技术和无容器实验技术，获得平衡熔体和深过冷液体中明确的粘度、密度和热容数据，其结果总结在本报告中。所有的合金在高、低温脆性上都表现出一致的差异。然而，与VIT1不同的是，在所有成分的结晶开始之后，对S-F转变的直接观察被掩盖了。初步工作已扩展到对VIT1和Zr58.5Cu15.6Ni12.8Al10.3Nb2.8(VIT106a)液体的量热和同步衍射研究。这种悬浮的原位研究可以区分结晶和L-L转变，以及监测从平衡熔体到玻璃化转变的液体结构因子S(Q)。在深过冷液中，这两种合金体系都出现了与S-F相变有关的热力学和结构异常。因此，拟议项目的目标是通过采用原位X射线衍射测量来深入了解与S-F相变相关的结构和热力学变化。结合以前的结果，这将使全面描述S-F转变的热力学、动力学和结构方面成为可能。

In recent years, studies of various multicomponent glass forming liquids have revealed a discrepancy between fragile liquid behavior in the equilibrium melt and strong liquid behavior in the glassy state. This has been attributed to a polymorphic liquid-liquid (L-L) transition between two different liquid phases, each exhibiting distinct thermodynamic and kinetic signatures. Using a Couette rheometer, Busch and coworkers observed a direct Strong-Fragile transition for Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (Vit1). To expand upon this work, the groups at the Chair of Metallic Materials in Saarbrücken and the Institute for Material Physics in Space in Köln have jointly investigated possible S-F transitions for select Zr-based metallic glass forming liquids. This project focused on obtaining unambiguous viscosity, density, and heat capacity data in the equilibrium melt and deeply undercooled liquid by comparing both conventional experimental techniques as well as containerless techniques, the results of which are summarized in this report. All of the alloys consistently showed the discrepancy in high and low temperature fragilities. However, unlike Vit1, direct observation of the S-F transition was obscured behind the onset of crystallization for all of the compositions. Preliminary works have been extended to calorimetric and synchrotron diffraction investigations of Vit1 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 (Vit106a) liquids. Such in-situ studies with levitation allow distinguishing between crystallization and the L-L transition as well as monitoring liquid structure factor S(Q) from equilibrium melt down to glass transition. For both alloys systems thermodynamic and structural anomalies associated with the S-F transition have been revealed in the deeply undercooled liquid. The goal of the proposed project is thus to gain insight into the structural and thermodynamic changes associated with the S-F transition by employing in-situ X-ray diffraction measurements. Combined with the previous results, this will enable a comprehensive description of the thermodynamic, kinetic, and structural aspects of the S-F transition.